Don't post gemini help text on PRs (#7072)

We all know and love Gemini but it doesn't need to poke us on every
single PR. I don't think the poke has caused anyone to request a review
who wasn't already going to ask for a review.

Author: sffc

.gemini/config.yaml

@@ -4,7 +4,7 @@ code_review:
   comment_severity_threshold: MEDIUM
   max_review_comments: -1
   pull_request_opened:
-    help: true
+    help: false
     summary: false
     code_review: false
 ignore_patterns: []